Process for preparing monosaccharide solution by means of acid gradient treatment of straw lignocellulose

Abstract

Disclosed in the present invention is a process for preparing a monosaccharide solution by means of acid gradient treatment of a straw lignocellulose. The process comprises the steps of: S1: performing a first acidolysis reaction on a lignocellulose biomass using an acid solution with a concentration of 50 wt% or above to obtain a first acidolysis solution; S2: uniformly mixing the first acidolysis solution with an organic solvent, and performing solid-liquid separation to obtain a glycan-containing residue; and S3: adding water and / or an acid solution to the glycan-containing residue to obtain a mixed solution with an acid concentration of 45 wt% or below, and performing a second acidolysis reaction to obtain a monosaccharide-containing reaction solution. In the present invention, pretreatment is performed at room temperature and atmospheric pressure without the need to provide additional energy, and various agents used in the pretreatment process are all recoverable, which greatly reduces the production cost. In addition, in the present invention, a relatively low liquid-solid ratio is used, monosaccharide can be directly obtained after the pretreatment, and finally a monosaccharide solution with a high and adjustable concentration is obtained, thereby avoiding a large amount of input in enzyme costs.

Description

A process for preparing monosaccharide solution by acid gradient treatment of straw-based lignocellulose Technical Field

[0001] The invention belongs to the field of biochemical engineering and bioenergy, and relates to a process for preparing a monosaccharide solution by subjecting straw-type lignocellulose to gradient acid treatment. Background Art

[0002] Bioenergy from lignocellulosic biomass is considered a suitable and potential alternative to fossil fuels due to their high greenhouse gas emissions. The agricultural, forestry, and industrial sectors are the main contributors to the availability of lignocellulosic biomass, with crop residues and forest residues being the most promising feedstocks. Lignocellulosic biomass is a potential source for the production of biofuels and biochemicals due to its abundance and low cost.

[0003] Lignocellulosic biomass materials are composed of three polymer layers, including cellulose, hemicellulose, and lignin. Because lignin is composed of complex aromatic polymers, it hinders the process efficiency in biofuel and biochemical production. Lignin components can be effectively removed through pretreatment technology to reduce its negative impact, but traditional pretreatment will inevitably lead to problems such as carbohydrate loss, and the residue obtained after pretreatment still requires the introduction of enzymes to obtain monosaccharide components, making the cost of biorefining still high. In traditional pretreatment processes, physical pretreatment has little effect when used alone and has high operating costs. Physical and chemical pretreatment requires high temperature, special reactors and expensive instruments. The biological pretreatment cycle is long, and the process will lead to the consumption of some carbohydrates due to the growth and utilization of the microorganisms themselves.

[0004] In order to overcome the key problems faced in the process of preparing monosaccharides from lignocellulosic biomass, many researchers have proposed corresponding solutions. For example, Chinese invention CN115341004A discloses a method for preparing monosaccharides from biomass raw materials, but this method requires two stages of adding enzyme preparations for monosaccharide preparation, and at the same time, the lignocellulosic biomass is subjected to at least one of steam explosion, cooking and puffing before the enzyme preparation is used. The overall process cost is high, the cycle is long, and the operation is cumbersome. Chinese invention CN101855368A discloses a method for preparing sugar products, but this method requires maintaining high temperature and high pressure during the acid treatment process, which brings a certain degree of challenge to the pretreatment process. Chinese invention CN114410850A discloses a comprehensive method for treating lignocellulosic materials, but this method requires a large amount of energy consumption and ignores the recovery and reuse of the acid used in the pretreatment process.

[0005] Therefore, developing economical, efficient and green methods to obtain monosaccharide solutions remains a key challenge facing lignocellulose conversion technology.

[0006] Summary of the Invention

[0007] The technical problem to be solved by the present invention is to address the shortcomings of the existing technology and provide a process for preparing a monosaccharide solution by acid gradient treatment of straw-based lignocellulose to solve the problems of sugar degradation into by-products affecting saccharification yield and producing microbial fermentation inhibitors in the previous non-grain bio-based sugar production process, as well as the energy consumption problem under harsh conditions of high temperature and high pressure.

[0008] In order to solve the above technical problems, the technical solutions adopted by the present invention are as follows:

[0009] The present invention discloses a process for preparing a monosaccharide solution by acid gradient treatment of straw-based lignocellulose, comprising the following steps:

[0010] S1: The lignocellulosic biomass is subjected to a first acid hydrolysis reaction catalyzed by an acid solution having a concentration of 50 wt% or more to obtain a first acid hydrolysis solution;

[0011] S2: mixing the first acid hydrolysis solution with an organic solvent, and performing solid-liquid separation to obtain a residue containing polysaccharides;

[0012] S3: adding water and / or an acid solution to the polysaccharide-containing residue to obtain a mixed solution having an acid concentration of less than 45 wt%, performing a second acid hydrolysis reaction to obtain a reaction solution containing monosaccharides, performing solid-liquid separation to obtain a monosaccharide-containing solution and a lignin precipitate; and treating the monosaccharide-containing solution in a simulated moving bed to obtain a monosaccharide solution and an acid solution;

[0013] S4: The acid-containing liquid phase obtained after the solid-liquid separation in step S2 is back-extracted with water, allowed to stand and then separated into layers to obtain an acid solution and an organic phase; the obtained organic phase is purified and returned to step S2 for use as an organic solvent; the obtained acid solution (including the acid solution in step S3) is concentrated to obtain an acid solution with a concentration of 50 wt% or more and condensed water or a low-concentration acid solution; the obtained acid solution with a concentration of 50 wt% or more is returned to step S1 for use as an acid solution; the obtained condensed water or low-concentration acid solution is returned to step S3.

[0014] In step S1, the lignocellulosic biomass includes straw-based lignocellulosic biomass; preferably, the straw-based lignocellulosic biomass is any one or a combination of wheat straw, corn straw, rice straw, sorghum straw, bagasse, corn cob, switchgrass, reed and rapeseed, preferably wheat straw.

[0015] In step S1, the acidic aqueous solution is an aqueous solution of an inorganic acid; preferably, the inorganic acid is any one or a combination of sulfuric acid, hydrochloric acid and phosphoric acid; preferably, the concentration of the acid in the acidic solution is 55wt%-95wt%, preferably 60wt%-90wt%, preferably 80wt%.

[0016] In step S1, the mass ratio of the lignocellulosic biomass to the acid in the acid solution is 1:0.5-2.5, preferably 1:1-2, and preferably 1:1.5.

[0017] In step S1, the reaction temperature of the first acid hydrolysis reaction is 20-30°C, preferably room temperature.

[0018] In step S1, the pressure of the first acid hydrolysis reaction is normal pressure.

[0019] In step S1, the first acid hydrolysis reaction is completed when the system has good fluidity. Taking 10 kg of straw as an example, the time required for the reaction to be completed is 1 hour.

[0020] In step S2, the organic solvent is any one or a combination of alcohol organic solvents, ketone organic solvents and tertiary amine organic solvents.

[0021] In step S2, the mass ratio of the first acid hydrolysis solution to the organic solvent is 1:1-5, preferably 1:2-4, preferably 1:2.5-3.5, preferably 1:3

[0022] In step S2, the purpose of mixing the first acid hydrolysis solution with the organic solvent is to extract and recover the acid in the first acid hydrolysis solution. The number of extractions is not limited and is adjusted according to actual conditions.

[0023] In step S3, the acid concentration of the mixed solution is 5 wt%-35 wt%, preferably 10 wt%-30 wt%, preferably 20 wt%.

[0024] In step S3, the temperature of the second acid hydrolysis reaction is 60-120°C, preferably 70-110°C, preferably 80-100°C, and preferably 90°C.

[0025] In step S3, the pressure of the second acid hydrolysis reaction is normal pressure.

[0026] In step S3, the second acid hydrolysis reaction time is 0.3 to 2.5 hours, preferably 0.4 to 2 hours, preferably 0.5 to 1.5 hours, and preferably 1 hour.

[0027] The polysaccharides described in the present invention mainly include glucan and xylan. Beneficial effects:

[0028] (1) The straw-based lignocellulosic biomass of the present invention is first pretreated (i.e., the first acid hydrolysis reaction) at room temperature and pressure, without the need for additional energy, and the various reagents used in the pretreatment process can be recycled, greatly reducing production costs.

[0029] (2) The straw-based lignocellulosic biomass of the present invention is first pretreated (i.e., primary acid hydrolysis) at room temperature and pressure, and then subjected to secondary acid hydrolysis, and the monosaccharide conversion rate obtained is significantly improved compared with traditional heating treatment, providing a new option for the construction of non-food bio-based sugar platforms.

[0030] (3) The present invention adopts a lower liquid-to-solid ratio, and monosaccharides can be directly obtained after pretreatment, and finally a high-concentration and controllable monosaccharide solution is obtained, avoiding the investment of a large amount of enzyme costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, and the above and / or other advantages of the present invention will become more apparent.

[0032] FIG1 is a flow chart of the pretreatment of straw-based lignocellulosic biomass according to an embodiment of the present invention.

[0033] FIG2 is a two-dimensional NMR image of the aromatic lignin obtained in Example 11 of the present invention.

[0034] FIG3 shows the types and distribution of polysaccharides obtained by a single acid hydrolysis in Example 11 of the present invention.

[0035] FIG4 is a monosaccharide solution obtained in Example 11 of the present invention. DETAILED DESCRIPTION

[0036] The experimental methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials are commercially available unless otherwise specified.

[0037] The straw-based lignocellulosic biomass raw material used in the following examples is wheat straw, which has a cellulose content of 34.92% by mass, a hemicellulose content of 22.58% by mass, and a lignin content of 23.03% by mass.

[0038] The simulated moving bed treatment conditions described in the following examples are: using strong acid styrene resin hydrogen type resin, a circulation flow rate of 75 ml / min, a feed flow rate of 25 ml / min, an elution reagent of water, and an elution flow rate of 75 ml / min.

[0039] The calculation method of glucose conversion rate and xylose conversion rate in the embodiment of the present invention is as follows:

[0040] Cellulose conversion % = C G *V / M G *100%

[0041] Hemicellulose conversion rate % = C X *V / M X *100%

[0042] C G : The concentration of glucose in the monosaccharide solution; C X : xylose concentration in monosaccharide solution; V: volume of monosaccharide solution; M G : Glucose mass in the straw input into the reaction; M X : The mass of xylose in the straw input into the reaction;

[0043] Example 1

[0044] A method for obtaining an acid-containing monosaccharide solution by acid treatment of straw-based lignocellulosic biomass comprises the following steps:

[0045] S1: Wheat straw (40-100 mesh) is mixed with a 60 wt% sulfuric acid aqueous solution. The straw can be added in batches or all at once. The mass ratio of wheat straw to sulfuric acid aqueous solution is 1:1. The reaction solution is subjected to a first acid hydrolysis reaction at room temperature and normal pressure until it has good fluidity to obtain a first acid hydrolysis solution.

[0046] S2: The first acid hydrolysis liquid obtained in step S1 is fully mixed with heptanol, wherein the mass ratio of the first acid hydrolysis liquid to heptanol is 1:3, and after mixing, solid-liquid separation is performed to obtain an acid-containing liquid phase and a residue containing polysaccharides and lignin.

[0047] S3: The residue containing polysaccharides and lignin obtained in step S2 is mixed with water and / or an acid solution to obtain a secondary acid hydrolysis mixture (acid concentration of 10 wt%). The secondary acid hydrolysis reaction is then carried out at atmospheric pressure and 80°C for 0.5 h. After the acid reaction is completed, the solid and liquid are separated to obtain an acid-containing monosaccharide solution and a lignin precipitate. The obtained acid-containing monosaccharide solution is treated in a simulated moving bed to obtain a monosaccharide solution and an acid solution.

[0048] S4: The acid-containing liquid phase obtained in step S2 is stripped with water, allowed to stand, and separated into layers to obtain an acid solution and an organic phase. The obtained organic phase is purified and returned to step S2 for use as an organic solvent. The obtained acid solution (including the acid solution obtained in step S3) is concentrated to obtain a >60 wt% acid solution and condensed water or a low-concentration acid solution; the obtained >60 wt% acid solution is returned to step S1 for use as the acid solution; the obtained condensed water or low-concentration acid solution is returned to step S3 for use as the secondary acid hydrolysis solvent.

[0049] After two stages of acid hydrolysis, the glucose conversion rate was 71.36% and the xylose conversion rate was 63.14%.

[0050] Example 2

[0051] A method for obtaining an acid-containing monosaccharide solution by acid treatment of straw-based lignocellulosic biomass comprises the following steps:

[0052] S1: Wheat straw (40-100 mesh) is mixed with a 60 wt% sulfuric acid aqueous solution. The straw can be added in batches or all at once. The mass ratio of wheat straw to sulfuric acid aqueous solution is 1:1. The reaction solution is subjected to a first acid hydrolysis reaction at room temperature and normal pressure until it has good fluidity to obtain a first acid hydrolysis solution.

[0053] S2: The first acid hydrolysis liquid obtained in step S1 is fully mixed with methyl ethyl ketone, wherein the mass ratio of the first acid hydrolysis liquid to methyl ethyl ketone is 1:3, and after mixing, solid-liquid separation is performed to obtain an acid-containing liquid phase and a residue containing polysaccharides and lignin.

[0054] S3: The residue containing polysaccharides and lignin obtained in step S2 is mixed with water and / or an acid solution to obtain a secondary acid hydrolysis mixture (acid concentration of 10 wt%). The secondary acid hydrolysis reaction is then carried out at atmospheric pressure and 80°C for 0.5 h. After the acid reaction is completed, the solid and liquid are separated to obtain an acid-containing monosaccharide solution and a lignin precipitate. The obtained acid-containing monosaccharide solution is treated in a simulated moving bed to obtain a monosaccharide solution and an acid solution.

[0055] S4: The acid-containing liquid phase obtained in step S2 is stripped with water, allowed to stand, and then separated into layers to obtain an acid solution and an organic phase. The obtained organic phase is purified and returned to step S2 for use as an organic solvent. The obtained acid solution (including the acid solution obtained in step S3) is concentrated to obtain a >60 wt% acid solution and condensed water or a low-concentration acid solution; the obtained >60 wt% acid solution is returned to step S1 for use as the acid solution; the obtained condensed water or low-concentration acid solution is returned to step S3 for use as the secondary acid hydrolysis solvent.

[0056] After two stages of acid hydrolysis, the glucose conversion rate was 66.89% and the xylose conversion rate was 52.66%.

[0057] Example 3

[0058] A method for obtaining an acid-containing monosaccharide solution by acid treatment of straw-based lignocellulosic biomass comprises the following steps:

[0059] S1: Wheat straw (40-100 mesh) is mixed with a 60 wt% sulfuric acid aqueous solution. The straw can be added in batches or all at once. The mass ratio of wheat straw to sulfuric acid aqueous solution is 1:1. The reaction solution is subjected to a first acid hydrolysis reaction at room temperature and normal pressure until it has good fluidity to obtain a first acid hydrolysis solution.

[0060] S2: The first acid hydrolysis liquid obtained in step S1 is fully mixed with tri(2-ethylhexyl)amine, wherein the mass ratio of the first acid hydrolysis liquid to tri(2-ethylhexyl)amine is 1:3, and after mixing, solid-liquid separation is performed to obtain an acid-containing liquid phase and a residue containing polysaccharides and lignin.

[0061] S3: The residue containing polysaccharides and lignin obtained in step S2 is mixed with water and / or an acid solution to obtain a secondary acid hydrolysis mixture (acid concentration of 10 wt%). The secondary acid hydrolysis reaction is then carried out at atmospheric pressure and 80°C for 0.5 h. After the acid reaction is completed, the solid and liquid are separated to obtain an acid-containing monosaccharide solution and a lignin precipitate. The obtained acid-containing monosaccharide solution is treated in a simulated moving bed to obtain a monosaccharide solution and an acid solution.

[0062] S4: The acid-containing liquid phase obtained in step S2 is stripped with water, allowed to stand, and then separated into layers to obtain an acid solution and an organic phase. The obtained organic phase is purified and returned to step S2 for use as an organic solvent. The obtained acid solution (including the acid solution obtained in step S3) is concentrated to obtain a >60 wt% acid solution and condensed water or a low-concentration acid solution; the obtained >60 wt% acid solution is returned to step S1 for use as the acid solution; the obtained condensed water or low-concentration acid solution is returned to step S3 for use as the secondary acid hydrolysis solvent.

[0063] After two stages of acid hydrolysis, the glucose conversion rate was 77.24% and the xylose conversion rate was 68.62%.

[0064] Example 4

[0065] A method for obtaining an acid-containing monosaccharide solution by acid treatment of straw-based lignocellulosic biomass comprises the following steps:

[0066] S1: Wheat straw (40-100 mesh) is mixed with a 90% wt% sulfuric acid aqueous solution. The straw can be added in batches or all at once. The mass ratio of wheat straw to sulfuric acid aqueous solution is 1:2. The reaction solution is subjected to a first acid hydrolysis reaction at room temperature and normal pressure until it has good fluidity to obtain a first acid hydrolysis solution.

[0067] S2: The first acid hydrolysis liquid obtained in step S1 is fully mixed with heptanol, wherein the mass ratio of the first acid hydrolysis liquid to heptanol is 1:3, and after mixing, solid-liquid separation is performed to obtain an acid-containing liquid phase and a residue containing polysaccharides and lignin.

[0068] S3: The residue containing polysaccharides and lignin obtained in step S2 is mixed with water and / or an acid solution to obtain a secondary acid hydrolysis mixture (acid concentration of 30 wt%). The secondary acid hydrolysis reaction is then carried out at atmospheric pressure and 100°C for 1.5 hours. After the acid reaction is completed, the solid and liquid are separated to obtain an acid-containing monosaccharide solution and a lignin precipitate. The obtained acid-containing monosaccharide solution is treated in a simulated moving bed to obtain a monosaccharide solution and an acid solution.

[0069] S4: The acid-containing liquid phase obtained in step S2 is stripped with water, allowed to stand, and then separated into layers to obtain an acid solution and an organic phase. The obtained organic phase is purified and returned to step S2 for use as an organic solvent. The obtained acid solution (including the acid solution obtained in step S3) is concentrated to obtain a >90 wt% acid solution and condensed water or a low-concentration acid solution; the obtained >90 wt% acid solution is returned to step S1 for use as the acid solution; the obtained condensed water or low-concentration acid solution is returned to step S3 for use as the secondary acid hydrolysis solvent.

[0070] After two stages of acid hydrolysis, the glucose conversion rate was 68.56% and the xylose conversion rate was 54.38%.

[0071] Example 5

[0072] A method for obtaining an acid-containing monosaccharide solution by acid treatment of straw-based lignocellulosic biomass comprises the following steps:

[0073] S1: Wheat straw (40-100 mesh) is mixed with a 90% wt% sulfuric acid aqueous solution. The straw can be added in batches or all at once. The mass ratio of wheat straw to sulfuric acid aqueous solution is 1:2. The reaction solution is subjected to a first acid hydrolysis reaction at room temperature and normal pressure until it has good fluidity to obtain a first acid hydrolysis solution.

[0074] S2: The first acid hydrolysis liquid obtained in step S1 is fully mixed with methyl ethyl ketone, wherein the mass ratio of the first acid hydrolysis liquid to methyl ethyl ketone is 1:3, and after mixing, solid-liquid separation is performed to obtain an acid-containing liquid phase and a residue containing polysaccharides and lignin.

[0075] S3: The residue containing polysaccharides and lignin obtained in step S2 is mixed with water and / or an acid solution to obtain a secondary acid hydrolysis mixture (acid concentration of 30 wt%). The secondary acid hydrolysis reaction is then carried out at atmospheric pressure and 100°C for 1.5 hours. After the acid reaction is completed, the solid and liquid are separated to obtain an acid-containing monosaccharide solution and a lignin precipitate. The obtained acid-containing monosaccharide solution is treated in a simulated moving bed to obtain a monosaccharide solution and an acid solution.

[0076] S4: The acid-containing liquid phase obtained in step S2 is stripped with water, allowed to stand, and then separated into layers to obtain an acid solution and an organic phase. The obtained organic phase is purified and returned to step S2 for use as an organic solvent. The obtained acid solution (including the acid solution obtained in step S3) is concentrated to obtain a >90 wt% acid solution and condensed water or a low-concentration acid solution; the obtained >90 wt% acid solution is returned to step S1 for use as the acid solution; the obtained condensed water or low-concentration acid solution is returned to step S3 for use as the secondary acid hydrolysis solvent.

[0077] After two stages of acid hydrolysis, the glucose conversion rate was 62.37% and the xylose conversion rate was 50.14%.

[0078] Example 6

[0079] A method for obtaining an acid-containing monosaccharide solution by acid treatment of straw-based lignocellulosic biomass comprises the following steps:

[0080] S1: Wheat straw (40-100 mesh) is mixed with a 90% wt% sulfuric acid aqueous solution. The straw can be added in batches or all at once. The mass ratio of wheat straw to sulfuric acid aqueous solution is 1:2. The reaction solution is subjected to a first acid hydrolysis reaction at room temperature and normal pressure until it has good fluidity to obtain a first acid hydrolysis solution.

[0081] S2: The first acid hydrolysis liquid obtained in step S1 is fully mixed with tri(2-ethylhexyl)amine, wherein the mass ratio of the first acid hydrolysis liquid to tri(2-ethylhexyl)amine is 1:3, and after mixing, solid-liquid separation is performed to obtain an acid-containing liquid phase and a residue containing polysaccharides and lignin.

[0082] S3: The residue containing polysaccharides and lignin obtained in step S2 is mixed with water and / or an acid solution to obtain a secondary acid hydrolysis mixture (acid concentration of 30 wt%). The secondary acid hydrolysis reaction is then carried out at atmospheric pressure and 100°C for 1.5 hours. After the acid reaction is completed, the solid and liquid are separated to obtain an acid-containing monosaccharide solution and a lignin precipitate. The obtained acid-containing monosaccharide solution is treated in a simulated moving bed to obtain a monosaccharide solution and an acid solution.

[0083] S4: The acid-containing liquid phase obtained in step S2 is stripped with water, allowed to stand, and then separated into layers to obtain an acid solution and an organic phase. The obtained organic phase is purified and returned to step S2 for use as an organic solvent. The obtained acid solution (including the acid solution obtained in step S3) is concentrated to obtain a >90 wt% acid solution and condensed water or a low-concentration acid solution; the obtained >90 wt% acid solution is returned to step S1 for use as the acid solution; the obtained condensed water or low-concentration acid solution is returned to step S3 for use as the secondary acid hydrolysis solvent.

[0084] After two stages of acid hydrolysis, the glucose conversion rate was 72.76% and the xylose conversion rate was 61.74%.

[0085] Example 7

[0086] A method for obtaining an acid-containing monosaccharide solution by acid treatment of straw-based lignocellulosic biomass comprises the following steps:

[0087] S1: Wheat straw (40-100 mesh) is mixed with a 60 wt% sulfuric acid aqueous solution. The straw can be added in batches or all at once. The mass ratio of wheat straw to sulfuric acid aqueous solution is 1:1. The reaction solution is subjected to a first acid hydrolysis reaction at room temperature and normal pressure until it has good fluidity to obtain a first acid hydrolysis solution.

[0088] S2: The first acid hydrolysis liquid obtained in step S1 is fully mixed with tri(2-ethylhexyl)amine, wherein the mass ratio of the first acid hydrolysis liquid to tri(2-ethylhexyl)amine is 1:3, and after mixing, solid-liquid separation is performed to obtain an acid-containing liquid phase and a residue containing polysaccharides and lignin.

[0089] S3: The residue containing polysaccharides and lignin obtained in step S2 is mixed with water and / or an acid solution to obtain a secondary acid hydrolysis mixture (acid concentration of 30 wt%). The secondary acid hydrolysis reaction is then carried out at atmospheric pressure and 100°C for 1.5 hours. After the acid reaction is completed, the solid and liquid are separated to obtain an acid-containing monosaccharide solution and a lignin precipitate. The obtained acid-containing monosaccharide solution is treated in a simulated moving bed to obtain a monosaccharide solution and an acid solution.

[0090] S4: The acid-containing liquid phase obtained in step S2 is stripped with water, allowed to stand, and then separated into layers to obtain an acid solution and an organic phase. The obtained organic phase is purified and returned to step S2 for use as an organic solvent. The obtained acid solution (including the acid solution obtained in step S3) is concentrated to obtain a >60 wt% acid solution and condensed water or a low-concentration acid solution; the obtained >60 wt% acid solution is returned to step S1 for use as the acid solution; the obtained condensed water or low-concentration acid solution is returned to step S3 for use as the secondary acid hydrolysis solvent.

[0091] After two stages of acid hydrolysis, the glucose conversion rate was 84.53% and the xylose conversion rate was 76.85%.

[0092] Example 8

[0093] A method for obtaining an acid-containing monosaccharide solution by acid treatment of straw-based lignocellulosic biomass comprises the following steps:

[0094] S1: Wheat straw (40-100 mesh) is mixed with a 90 wt% sulfuric acid aqueous solution. The straw can be added in batches or all at once. The mass ratio of wheat straw to sulfuric acid aqueous solution is 1:2. The reaction solution is subjected to a first acid hydrolysis reaction at room temperature and normal pressure until it has good fluidity to obtain a first acid hydrolysis solution.

[0095] S2: The first acid hydrolysis liquid obtained in step S1 is fully mixed with tri(2-ethylhexyl)amine, wherein the mass ratio of the first acid hydrolysis liquid to tri(2-ethylhexyl)amine is 1:3, and after mixing, solid-liquid separation is performed to obtain an acid-containing liquid phase and a residue containing polysaccharides and lignin.

[0096] S3: The residue containing polysaccharides and lignin obtained in step S2 is mixed with water and / or an acid solution to obtain a secondary acid hydrolysis mixture (acid concentration of 10 wt%). The secondary acid hydrolysis reaction is then carried out at atmospheric pressure and 80°C for 0.5 h. After the acid reaction is completed, the solid and liquid are separated to obtain an acid-containing monosaccharide solution and a lignin precipitate. The obtained acid-containing monosaccharide solution is treated in a simulated moving bed to obtain a monosaccharide solution and an acid solution.

[0097] S4: The acid-containing liquid phase obtained in step S2 is stripped with water, allowed to stand, and then separated into layers to obtain an acid solution and an organic phase. The obtained organic phase is purified and returned to step S2 for use as an organic solvent. The obtained acid solution (including the acid solution obtained in step S3) is concentrated to obtain a >90 wt% acid solution and condensed water or a low-concentration acid solution; the obtained >90 wt% acid solution is returned to step S1 for use as the acid solution; the obtained condensed water or low-concentration acid solution is returned to step S3 for use as the secondary acid hydrolysis solvent.

[0098] After two stages of acid hydrolysis, the glucose conversion rate was 88.21% and the xylose conversion rate was 82.46%.

[0099] Example 9

[0100] A method for obtaining an acid-containing monosaccharide solution by acid treatment of straw-based lignocellulosic biomass comprises the following steps:

[0101] S1: Wheat straw (40-100 mesh) is mixed with an aqueous sulfuric acid solution having a mass percentage concentration of 80 wt %. The straw can be added in batches or all at once, wherein the mass ratio of wheat straw to aqueous sulfuric acid solution is 1:1.5. The reaction solution is subjected to a first acid hydrolysis reaction at room temperature and normal pressure until it has good fluidity to obtain a first acid hydrolysis solution.

[0102] S2: The first acid hydrolysis liquid obtained in step S1 is fully mixed with heptanol, wherein the mass ratio of the first acid hydrolysis liquid to heptanol is 1:3, and after mixing, solid-liquid separation is performed to obtain an acid-containing liquid phase and a residue containing polysaccharides and lignin.

[0103] S3: The residue containing polysaccharides and lignin obtained in step S2 is mixed with water and / or an acid solution to obtain a secondary acid hydrolysis mixture (acid concentration of 20 wt%). The secondary acid hydrolysis reaction is then carried out at atmospheric pressure and 90°C for 1 hour. After the acid reaction is completed, the solid and liquid are separated to obtain an acid-containing monosaccharide solution and a lignin precipitate. The obtained acid-containing monosaccharide solution is treated in a simulated moving bed to obtain a monosaccharide solution and an acid solution.

[0104] S4: The acid-containing liquid phase obtained in step S2 is stripped with water, allowed to stand, and then separated into layers to obtain an acid solution and an organic phase. The obtained organic phase is purified and returned to step S2 for use as an organic solvent. The obtained acid solution (including the acid solution obtained in step S3) is concentrated to obtain an acid solution with a concentration of >80 wt% and condensed water or a low-concentration acid solution; the obtained acid solution with a concentration of >80 wt% is returned to step S1 for use as the acid solution; the obtained condensed water or low-concentration acid solution is returned to step S3 for use as the secondary acid hydrolysis solvent.

[0105] After two stages of acid hydrolysis, the glucose conversion rate was 85.64% and the xylose conversion rate was 78.49%.

[0106] Example 10

[0107] A method for obtaining an acid-containing monosaccharide solution by acid treatment of straw-based lignocellulosic biomass comprises the following steps:

[0108] S1: Wheat straw (40-100 mesh) is mixed with an aqueous sulfuric acid solution having a mass percentage concentration of 80 wt %. The straw can be added in batches or all at once, wherein the mass ratio of wheat straw to aqueous sulfuric acid solution is 1:1.5. The reaction solution is subjected to a first acid hydrolysis reaction at room temperature and normal pressure until it has good fluidity to obtain a first acid hydrolysis solution.

[0109] S2: The first acid hydrolysis liquid obtained in step S1 is fully mixed with methyl ethyl ketone, wherein the mass ratio of the first acid hydrolysis liquid to methyl ethyl ketone is 1:3, and after mixing, solid-liquid separation is performed to obtain an acid-containing liquid phase and a residue containing polysaccharides and lignin.

[0110] S3: The residue containing polysaccharides and lignin obtained in step S2 is mixed with water and / or an acid solution to obtain a secondary acid hydrolysis mixture (acid concentration of 20 wt%). The secondary acid hydrolysis reaction is then carried out at atmospheric pressure and 90°C for 1 hour. After the acid reaction is completed, the solid and liquid are separated to obtain an acid-containing monosaccharide solution and a lignin precipitate. The obtained acid-containing monosaccharide solution is treated in a simulated moving bed to obtain a monosaccharide solution and an acid solution.

[0111] S4: The acid-containing liquid phase obtained in step S2 is stripped with water, allowed to stand, and then separated into layers to obtain an acid solution and an organic phase. The obtained organic phase is purified and returned to step S2 for use as an organic solvent. The obtained acid solution (including the acid solution obtained in step S3) is concentrated to obtain an acid solution with a concentration of >80 wt% and condensed water or a low-concentration acid solution; the obtained acid solution with a concentration of >80 wt% is returned to step S1 for use as the acid solution; the obtained condensed water or low-concentration acid solution is returned to step S3 for use as the secondary acid hydrolysis solvent.

[0112] After two stages of acid hydrolysis, the glucose conversion rate was 83.42% and the xylose conversion rate was 75.93%.

[0113] Example 11

[0114] A method for obtaining an acid-containing monosaccharide solution by acid treatment of straw-based lignocellulosic biomass comprises the following steps:

[0115] S1: Wheat straw (40-100 mesh) is mixed with an aqueous sulfuric acid solution having a mass percentage concentration of 80 wt %. The straw can be added in batches or all at once, wherein the mass ratio of wheat straw to aqueous sulfuric acid solution is 1:1.5. The reaction solution is subjected to a first acid hydrolysis reaction at room temperature and normal pressure until it has good fluidity to obtain a first acid hydrolysis solution.

[0116] S2: The first acid hydrolysis liquid obtained in step S1 is fully mixed with tri(2-ethylhexyl)amine, wherein the mass ratio of the first acid hydrolysis liquid to tri(2-ethylhexyl)amine is 1:3, and after mixing, solid-liquid separation is performed to obtain an acid-containing liquid phase and a residue containing polysaccharides and lignin.

[0117] S3: The residue containing polysaccharides and lignin obtained in step S2 is mixed with water and / or an acid solution to obtain a secondary acid hydrolysis mixture (acid concentration of 20 wt%). The secondary acid hydrolysis reaction is then carried out at atmospheric pressure and 90°C for 1 hour. After the acid reaction is completed, the solid and liquid are separated to obtain an acid-containing monosaccharide solution and a lignin precipitate. The obtained acid-containing monosaccharide solution is treated in a simulated moving bed to obtain a monosaccharide solution and an acid solution.

[0118] S4: The acid-containing liquid phase obtained in step S2 is stripped with water, allowed to stand, and then separated into layers to obtain an acid solution and an organic phase. The obtained organic phase is purified and returned to step S2 for use as an organic solvent. The obtained acid solution (including the acid solution obtained in step S3) is concentrated to obtain an acid solution with a concentration of >80 wt% and condensed water or a low-concentration acid solution; the obtained acid solution with a concentration of >80 wt% is returned to step S1 for use as the acid solution; the obtained condensed water or low-concentration acid solution is returned to step S3 for use as the secondary acid hydrolysis solvent.

[0119] After two acid hydrolysis steps, the glucose conversion rate reached 91.58%, the xylose conversion rate reached 85.29%, and the total sugar concentration in the final monosaccharide solution reached 109.61 g / L.

[0120] Example 12

[0121] A method for obtaining an acid-containing monosaccharide solution by acid-treating straw-based lignocellulosic biomass is similar to that of Example 1, except that a different solvent is used for the treatment.

[0122] Figure 2 shows the aromatic structure of the residual lignin components after secondary acid hydrolysis, which can be recycled for the preparation of bio-based fertilizers.

[0123] Figure 3 shows the types and distribution of polysaccharides obtained by single acid hydrolysis, which are mainly glucan and xylan.

[0124] FIG4 is a monosaccharide solution obtained by the present invention, the components of which are mainly glucose and xylose among monosaccharides.

[0125] The present invention provides a method and concept for obtaining an acid-containing monosaccharide solution by acid-treating straw-based lignocellulosic biomass. There are numerous methods and approaches for implementing this technical solution. The above is merely a preferred embodiment of the present invention. It should be noted that those skilled in the art may make various improvements and modifications without departing from the principles of the present invention, and such improvements and modifications are also within the scope of protection of the present invention. Any components not specified in this embodiment may be implemented using existing technologies.

Claims

1. A method for preparing monosaccharides from lignocellulosic biomass, characterized in that: The steps include: S1: The lignocellulosic biomass is subjected to a first acid hydrolysis reaction catalyzed by an acid solution having a concentration of 50 wt % or more to obtain a first acid hydrolysis solution; S2: mixing the first acid hydrolysis solution with an organic solvent, separating the solid and the liquid, and obtaining a residue containing polysaccharides; S3: adding water and / or acid solution to the polysaccharide-containing residue to obtain a mixed solution having an acid concentration of 45 wt % or less, and performing a second acid hydrolysis reaction to obtain a reaction solution containing monosaccharides.

2. The method according to claim 1, characterized in that In step S1, the lignocellulosic biomass includes straw-based lignocellulosic biomass; preferably, the straw-based lignocellulosic biomass is any one or a combination of wheat straw, corn straw, rice straw, sorghum straw, bagasse, corn cob, switchgrass, reed and rapeseed.

3. The method according to claim 1, characterized in that In step S1, the acidic aqueous solution is an aqueous solution of an inorganic acid; preferably, the inorganic acid is any one or a combination of sulfuric acid, hydrochloric acid and phosphoric acid; Preferably, the concentration of the acid in the acidic solution is 55 wt%-95 wt%, preferably 60 wt%-90 wt%.

4. The method according to claim 1, characterized in that In step S1, the mass ratio of the lignocellulosic biomass to the acid in the acid solution is 1:0.5-2.5, preferably 1:1-2; preferably, the reaction temperature of the first acid hydrolysis reaction is 20-30°C, preferably room temperature; preferably, the pressure of the first acid hydrolysis reaction is normal pressure.

5. The method according to claim 1, characterized in that: In step S2, the organic solvent is any one or a combination of alcohol organic solvents, ketone organic solvents and tertiary amine organic solvents.

6. The method according to claim 1, characterized in that In step S2, the mass ratio of the first acid hydrolysis solution to the organic solvent is 1:1-5, preferably 1:2-4, and preferably 1:2.5-3.

5.

7. The method according to claim 1, characterized in that In step S3, the acid concentration of the mixed solution is 5wt%-35wt%, preferably 10wt%-30wt%.

8. The method according to claim 1, characterized in that In step S3, the temperature of the second acid hydrolysis reaction is 60-120°C, preferably 70-110°C, preferably 80-100°C; preferably, the pressure of the second acid hydrolysis reaction is normal pressure; preferably, the time of the second acid hydrolysis reaction is 0.3-2.5h, preferably 0.4-2h, preferably 0.5-1.5h.

9. The method according to claim 1, characterized in that: In step S3, the monosaccharide-containing reaction liquid is subjected to solid-liquid separation to obtain a monosaccharide-containing solution and a lignin precipitate; the monosaccharide-containing solution is treated by a simulated moving bed to obtain a monosaccharide solution and an acid solution.

10. The method according to claim 1, characterized in that The method further comprises: S4: adding water to the acid-containing liquid phase obtained after the solid-liquid separation in step S2 for back extraction, standing and separating the phases to obtain an acid solution and an organic phase.

11. The method according to claim 10, characterized in that The organic phase obtained in step S4 is purified and returned to step S2 for use as an organic solvent.

12. The method according to claim 9 or 10, characterized in that: The acid solution obtained in step S4 and / or S3 is concentrated to obtain an acid solution with a concentration of 50 wt% or more and condensed water or a low-concentration acid solution; preferably, the obtained acid solution with a concentration of 50 wt% or more is returned to step S1 for use as an acid solution; the obtained condensed water or low-concentration acid solution is returned to step S3.

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